The present invention relates generally to the technical field of fiber optics, and, more particularly, to free-space, reflective Nxc3x97N fiber optic switches.
A dramatic increase in telecommunications during recent years, which may be attributed largely to increasing Internet communications, has required rapid introduction and commercial adoption of innovations in fiber optic telephonic communication systems. For example, recently fiber optic telecommunication systems have been introduced and are being installed for transmitting digital telecommunications concurrently on 4, 16, 32, 64 or 128 different wavelengths of light that propagate along a single optical fiber. While multi-wavelength fiber optic telecommunications dramatically increases the bandwidth of a single optical fiber, that bandwidth increase is available only at both ends of the optical fiber, e.g. between two cities. When light transmitted into one end of the optical fiber arrives at the other end of the optical fiber, there presently does not exist a flexible, modular, compact, Nxc3x97N fiber optic switch which permits automatically forwarding light received at one end of the optical fiber onto a selected one of several different optical fibers which will carry the light onto yet other destinations.
Historically, when telecommunications were transmitted by electrical signals via pairs copper wires, at one time a human being called a telephone operator sat at a manually operated switchboard and physically connected an incoming telephone call, received on one pair of copper wires, that were attached to a plug, to another pair of copper wires, that were attached to a socket, to complete the telephone circuit. The telephone operator""s task of manually interconnecting pairs of wires from two (2) telephones to establish the telephone circuit was first replaced by an electromechanical device, called a crossbar switch, which automated the operator""s manual task in response to telephone dialing signals. During the past forty years, the electro-mechanical crossbar switch for electrical telecommunications has been replaced by electronic switching systems.
Presently, switches for fiber optic telephonic communications exist which perform functions for fiber optic telephonic communications analogous to or the same as the crossbar switch and electronic switching systems perform for electrical telephonic communications. However, the presently available fiber optic switches are far from ideal. That is, existing fiber optic telecommunications technology lacks a switch that performs the same function for optical telecommunications as that performed by electronic switching systems for large numbers of optical fibers.
One approach used in providing a 256xc3x97256 switch for fiber optic telecommunications first converts light received from a incoming optical fiber into an electrical signal, then transmits the electrical signal through an electronic switching network. The output signal from that electronic switching network is then used to generate a second beam of light that then passes into an output optical fiber. As those familiar with electronics and optical fiber telecommunications recognize, the preceding approach for providing a 256xc3x97256 fiber optic switch is physically very large, requires electrical circuits which process extremely high-speed electronic signals, and is very expensive.
Attempting to avoid complex electronic circuits and conversions between light and electronic signals, various proposals exist for assembling a fiber optic switch that directly couples a beam of light from one optical fiber into another optical fiber. One early attempt to provide a fiber optic switch, analogous to the electrical crossbar switch, mimics with machinery the actions of a telephone operator only with optical fibers rather than for pairs of copper wires. U.S. Pat. No. 4,886,335 entitled xe2x80x9cOptical Fiber Switch Systemxe2x80x9d that issued Dec. 12, 1989, includes a conveyor that moves ferrules attached to ends of optical fibers. The conveyer moves the ferrule to a selected adapter and plugs the ferrule into a coupler/decoupler included in the adapter. After the ferrule is plugged into the coupler/decoupler, light passes between the optical fiber carried in the ferrule and an optical fiber secured in the adapter.
U.S. Pat. No. 5,864,463 entitled xe2x80x9cMiniature 1xc3x97N Electromechanical Optical Switch And Variable Attenuatorxe2x80x9d which issued Jan. 26, 1999, (xe2x80x9cthe ""463 patentxe2x80x9d) describes another mechanical system for selectively coupling light between one optical fiber and one of a number of optical fibers. This patent discloses selectively coupling light between one optical fiber and a selected optical fiber by mechanically moving an end of one optical fiber along a linear array of ends of the other optical fibers. The 1xc3x97N switch uses a mechanical actuator to coarsely align the end of the one optical fiber to a selected one of the other optical fibers within 10 xcexcm. The 1xc3x97N switch, using light reflected back into the moving optical fiber from the immediately adjacent end of the selected optical fiber, then more precisely aligns the end of the input optical fiber to the output optical fiber. U.S. Pat. No. 5,699,463 entitled xe2x80x9cMechanical Fiber Optic Switchxe2x80x9d that issued Dec. 16, 1997, also aligns an end of one optical fiber to one of several other optical fibers assembled as a linear array, but interposes a lens between ends of the two optical fibers.
U.S. Pat. No. 5,524,153 entitled xe2x80x9cOptical Fiber Switching System And Method Of Using Samexe2x80x9d that issued Jun. 4, 1996, (xe2x80x9cthe ""153 patentxe2x80x9d) disposes two (2) optically opposed groups of optical fiber switching units adjacent to each other. Each switching unit is capable of aligning any one of its optical fibers with any one of the optical fibers of the optically opposed group of switching units. Within the switching unit, an end of each optical fiber is positioned adjacent to a beamforming lens, and is received by a two-axis piezoelectric bender. The two-axis piezoelectric bender is capable of bending the fiber so light emitted from the fiber points at a specific optical fiber in the optically opposed group of switching units. Pulsed light generated by radiation emitting devices (xe2x80x9cREDsxe2x80x9d) associated with each optical fiber pass from the fiber to the selected optical fiber in the opposing group. The pulsed light from the RED received by the selected optical fiber in the opposing group is processed to provide a signal that is fed back to the piezoelectric bender for pointing light from the optical fiber directly at the selected optical fiber.
Rather than mechanically effecting alignment of a beam of light from one optical fiber to another optical fiber either by translating or by bending one or both optical fibers, optical switches have been proposed that employ micromachined moving mirror arrays to selectively couple light emitted from an input optical fiber to an output optical fiber. Papers presented at OFC/IOOC ""99, Feb. 21-26, 1999, describe elements that could be used to fabricate a three (3) stage fully non-blocking fiber optic switch, depicted graphically in FIG. 1. This fiber optic switch employs moving mirror arrays in which each polysilicon mirror can selectively reflect light at a 90xc2x0 angle. In this proposed fiber optic switch, rows of relatively small 32xc3x9764 optical switching arrays 52ai (i=1, 2 . . . 32) and 52bk (k=1, 2 . . . 32) receive light from or transmit light to thirty-two (32) input or output optical fibers 54an and 54bn. Thirty-two groups of sixty-four (64) optical fibers 56al,m and 56bl,m carry light between each of the 32xc3x9764 optical switching arrays 52ai and 52bk and one of sixty-four 32xc3x9732 optical switching arrays 58j (j=1, 2 . . . 64).
The complexity of the fiber optic switch illustrated in FIG. 1 is readily apparent. For example, a 1024xc3x971024 fiber optic switch assembled in accordance with that proposal requires 4096 individual optical fibers for interconnecting between the 32xc3x9764 optical switching arrays 52ai and 52bk and the 32xc3x9732 optical switching arrays 58j. Moreover, the 32xc3x9764 optical switching arrays 52ai and 52bk and 32xc3x9732 optical switching arrays 58j require a total of 196,608 micromachined mirrors.
The polysilicon mirrors proposed for the fiber optic switch illustrated in FIG. 1 are curved rather than optically flat. Furthermore, while those mirrors possess adequate thermal dissipation for switching a single 0.3 mW wavelength of light and perhaps even a few such wavelengths, they are incapable of switching even ten (10) or twenty (20) such wavelengths. However, as described above fiber optic telecommunications systems are already transmitting many more than twenty (20) wavelengths over a single optical fiber, and, if not already, will soon be transmitting hundreds of wavelengths. If instead of a single wavelength of light one optical fiber carries 300 different wavelengths of light each having a power of 0.3 mW, then 100 mW of power impinges upon the polysilicon mirror proposed for this fiber optic switch. If the polysilicon mirror reflects 98.5% of that light, the mirror must absorb substantially all of the remainder, i.e. 1.5 mW of power. Absorption of 1.5 mW of power would likely heat the thermally non-conductive polysilicon mirror to unacceptable temperatures which would further degrade mirror flatness.
The present invention provides a fiber optic switch capable of concurrently coupling incoming beams of light carried on more than 1,000 individual optical fibers to more than 1,000 outgoing optical fibers.
An object of the present invention is to provide a simpler fiber optic switch that is capable of switching among a large number of incoming and outgoing beams of light carried on optical fibers.
Another object of the present invention is to provide an efficient fiber optic switch that is capable of switching among a large number of incoming and outgoing beams of light carried on optical fibers.
Another object of the present invention is to provide a fiber optic switch which has low cross-talk between communication channels.
Another object of the present invention is to provide a fiber optic switch which has low cross-talk between communication channels during switching thereof.
Another object of the present invention is to provide an highly reliable fiber optic switch.
Another object of the present invention is to provide a fiber optic switch that does not exhibit dispersion.
Another object of the present invention is to provide a fiber optic switch that is not polarization dependent.
Another object of the present invention is to provide a fiber optic switch that is fully transparent.
Another object of the present invention is to provide a fiber optic switch that does not limit the bitrate of fiber optic telecommunications passing through the switch.
Briefly the present invention is a fiber optic switch that includes a fiber optic switching module that receives and fixes ends of optical fibers. In addition to receiving and fixing ends of optical fibers, the fiber optic switching module includes a plurality of reflective light beam deflectors which may be selected as pairs to be oriented responsive to drive signals for coupling a beam of light between a pair of optical fibers fixed in the fiber optic switching module. The fiber optic switching module also produces orientation signals from each light beam deflector which indicate its orientation.
In addition to the fiber optic switch module, the fiber optic switch also includes at least one portcard that supplies the drive signals to the fiber optic switching module for orienting at least one light beam deflector included therein. Furthermore, the portcard also receives the orientation signals produced by that light beam deflector together with coordinates that specify an orientation for the light beam deflector. The portcard compares the received coordinates with the orientation signals received from the light beam deflector and adjusts the drive signals supplied to the fiber optic switching module to reduce any difference between the received coordinates and the orientation signals.
In a preferred embodiment, the fiber optic switching module of the fiber optic switch includes a first and a second group of optical fiber receptacles which are separated from each other at opposite ends of a free space optical path. Each of these groups of optical fiber receptacles are adapted for receiving and fixing ends of optical fibers. The fiber optic switching module includes lenses juxtaposed with ends of optical fibers fixed respectively at the first and second groups and disposed along the optical path between the groups. Each of these lenses are respectively disposed with respect to an end of an associated optical fiber of the first or second group so that beams of light as may be emitted from the end of the optical fiber pass through the immediately adjacent lens to propagate as quasi-collimated beams through the optical path from the lens toward the second or first group of optical fiber receptacles.
The preferred embodiment of the fiber optic switch also includes first and second sets of reflective light beam deflectors that are both disposed along the optical path between the groups of optical fiber receptacles. Each of the sets of light beam deflectors are associated with one of the groups of optical fiber receptacles and have a number of light beam deflectors that equals the number of optical fibers in the group with which it is associated. Each of the light beam deflectors in the first or the second set is:
1. associated with one of the optical fibers in the associated group of optical fiber receptacles;
2. along the optical path so the quasi-collimated beam of light as may be emitted from the lens associated with the optical fiber impinges upon the light beam deflector to be reflected therefrom through the optical path; and
3. energizable by drive signals supplied to the fiber optic switching module to be oriented for reflecting the quasi-collimated beam of light as may be emitted from the associated optical fiber to also reflect off a selected one of the light beam deflectors in the second or the first set.
In this way a pair of light beam deflectors, one light beam deflector of the pair belonging to the first set and one belonging to the second set, may be selected and oriented by the drive signals supplied to them to couple a quasi-collimated beam of light propagating through the optical path from the end of one optical fiber fixed in an optical fiber receptacle either of the first or of the second group to reflect sequentially off the pair of energized light beam deflectors into a selected one of the optical fiber receptacles so as to enter an optical fiber as may be fixed at the second or at the first group of optical fiber receptacles.
In a preferred embodiment the portcard of the fiber optic switch includes a driver circuit for supplying the drive signals to the fiber optic switching module for orienting at least one light beam deflector included in the fiber optic switching module. The portcard also includes a dual axis servo that receives coordinates which specify an orientation for the light beam deflector, and also receives the orientation signals produced by that light beam deflector. The portcard compares the received coordinates with the orientation signals received from the light beam deflector and adjusts the drive signals supplied to the fiber optic switching module to reduce any difference between the received coordinates and the orientation signals.
These and other features, objects and advantages will be understood or apparent to those of ordinary skill in the art from the following detailed description of the preferred embodiment as illustrated in the various drawing figures.